Reciprocating internal combustion (IC) engines are known for converting chemical energy, which is stored in a fuel supply, into mechanical shaft power. A fuel-oxidizer mixture is received in a variable volume of an IC engine defined by a piston translating within a cylinder bore. The fuel-oxidizer mixture burns inside the variable volume to convert chemical energy from the mixture into heat. In turn, expansion of the combustion products within the variable volume performs work on the piston, which may be transferred to an output shaft of the IC engine.
In conventional direct injection compression ignition engines, most if not all of the fuel is injected into the variable volume a short ignition delay time before the desired ignition timing. In other compression ignition engines, such as homogeneous charge compression ignition (HCCI) engines, a fuel is substantially premixed with an oxidizer and ignited by compression within the variable volume. Premixing of the fuel and oxidizer may be achieved by injecting the fuel into the oxidizer upstream of the variable volume, injecting the fuel into the variable volume relatively early in a compression stroke, or combinations thereof.
Engines operating with fuels having relatively low Cetane values, such as natural gas, may benefit from supplemental ignition sources such as a spark plug or a pilot injection of a fuel having a relatively high Cetane value, such as distillate diesel fuel. For example, an engine may substantially premix a low-Cetane fuel with an oxidizer within a variable volume and then ignite the mixture of low-Cetane fuel and oxidizer by directly injecting an amount of high-Cetane fuel into the variable volume a short time delay before the desired ignition timing. In such a dual fuel configuration, compression ignition of the high-Cetane fuel may effect or promote ignition of the mixture of the low-Cetane fuel and the oxidizer.
In some dual fuel engine systems, a gaseous fuel is a low-Cetane fuel and a liquid fuel is a high-Cetane fuel, and injection of the liquid fuel and the gaseous fuel is controlled by two separate needle checks within a fuel injector connected to both a gaseous fuel common rail and a liquid fuel common rail. Where concentric needle checks are used, an outer check may be used to selectively open and close a gaseous fuel outlet, and an inner check may be used to selectively open and close a liquid fuel outlet. In other systems, adjacent rather than coaxial needle checks are used. An adjacent needle check design, which employs hydraulic control pressure from a liquid fuel common rail applied to each of the needle checks may be used to control opening and closing of a corresponding nozzle outlet.
U.S. Pat. No. 7,627,416 (the '416 patent) purports to describe a dual fuel common rail design in which liquid diesel fuel and natural gas fuel are both injected from a single fuel injector associated with each engine cylinder. The '416 patent recognizes that there may be instances in which the engine will need to operate solely on liquid diesel fuel due to exhaustion of the natural gas fuel supply or possibly due to a fault in the natural gas fuel supply portion of the system. However, problems and challenges associated with disparate liquid fuel pressure and the gaseous fuel pressure, such as leakage between the liquid fuel system and the gaseous fuel system across the needle checks, are neither recognized nor addressed in the '416 patent. Accordingly, improved dual fuel injectors are desired to address the aforementioned problems and/or other problems known in the art.
It will be appreciated that this background description has been created to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves known in the art.